See full version: Aluminum Workshop: Tips for repairing cracks
Q: What is the best way to repair cracks? Is it better to use GTAW or GMAW? I have heard that sometimes the crack will grow while being repaired. Is this true? Are there any tricks to avoid this? Is repairing cracks in aluminum any different than repairing cracks in other materials?
Is aluminum different? Yes, in one very important way. Remember that aluminum forms an oxide layer almost immediately upon exposure to air. The crack’s surface also has an oxide layer. If you try to repair the crack merely by welding over it, the oxide layer will keep the crack from mending, and it will still be there after welding. Therefore, to repair a crack in aluminum, you must first excavate the cracked area with a grinding wheel or burr and completely remove the crack. Only then can you repair weld it.
A: Yes, it’s true that sometimes cracks grow while being repaired. This is because welding locally heats and expands the metal, which causes very high stresses around the repair area. You can reduce these stresses by preheating the metal to be welded. If you do, remember not to preheat any of the heat-treatable alloys above 250 degrees F. It also helps to drill holes at the end of the crack. The round hole distributes the stresses more evenly and should keep the crack from growing. more
check with your local radiator shop. my guy welds aluminum boats all the time for $35 per hour more
Alot of that depends on execution there force. If you do decide to go the patch route, Once you get the patch in the shape that you want it, you'll want the 5200 to have something to grab. Sand the surfaces and clean them with acetone..and try to avoid touching them. You could take it a step further and do a chromate conversion (Alodine) and/or spray with Zinc chromate. [links]
typical weld would be to j-groove the crack and weld. then hot-flow the weld here
5052 is soft, no need to heat with a torch to bend. here
As discussed above, two dissimilar metals can set up corrosion. Epoxy barrier coats between the aluminum hull and bottom paint will effectively prevent this. [links]
Aluminum boats are known for being durable and well constructed. With a relatively low amount of maintenance, aluminum boats can last for years. [links]
Especially when purchasing used aluminum boats, care should be taken to inspect the boat’s shaft tube. Many aluminum boats suffer from corrosion in the shaft tube.
Another cause of corrosion is electrolysis from faulty wiring. Any currents that flow from the aluminum hull to other metals in the area will cause corrosion.
It is possible to drill rivets out, apply sealant, and replace them with nuts and bolts. more
There are several competent welders on this site, but (to my knowledge) not one of them is a freaking mindreader. more
Not trying to pick on you, but with 50 posts you should know better than ask such a question as you asked in the original post.
Being a welder (even a hobbiest) is knowing one's limitations. here
Have your "friend" take his boat to someone that knows what he's doing.